docs: def getAudioData(self):
      """ Fetch the audio data. """
      with self.preload_mutex:
        cache_url = self.buildUrl(cache_friendly=True)
        if cache_url in __class__.cache:
          logging.getLogger().debug("Got data for URL '%s' from cache" % (cache_url))
          audio_data = __class__.cache[cache_url]
          assert(audio_data)
        else:
          real_url = self.buildUrl()
          audio_data = self.download(real_url)
          assert(audio_data)
          __class__.cache[cache_url] = audio_data
      return audio_data